1. Field of the Invention
The present systems and methods relate generally to enhancing the performance of electric motors operable at a variety of speeds and, more specifically, to enhancing the accuracy of torque calculations to operate such motors. The described systems and methods may be used by a variety of applications, for example, with a powertrain related-system or a traction drive system.
2. Description of the Related Art
The xe2x80x9cfuelxe2x80x9d powering a field oriented induction motor is current. This current may be divided into two components, torque current and flux current. Torque current may be viewed as that component of the current which generates motive force, or torque. Flux current may be viewed as that component of the current which generates magnetic flux in the rotor. Shaft torque and rotor flux are related, with shaft torque being proportional to the product of rotor flux times torque current.
A knowledge of the level of torque produced by a field oriented induction motor during operation is helpful to the effective operation of a variable speed system, requiring precise control, such as a traction drive system or compressor drive system, as will be readily apparent to those skilled in the relevant art. Typically, the torque produced by a field oriented induction motor is calculated using two equations, one for low-speed operation and one for high-speed operation. Under high-speed operating conditions, torque current, back-EMF voltage, and speed are used to estimate torque. Under low-speed operating conditions, the back-EMF voltage is too low to be used to estimate torque. Thus, torque current, flux current, and motor inductance are used. These equations, however, break down in the xe2x80x9cin-betweenxe2x80x9d or interface range, resulting in inaccurate torque calculations. These calculations, relied upon by the traction drive system, may lead to diminished performance of the system.
The present systems and methods overcome the problems discussed above and enhance the performance of electric motors operable at a variety of speeds, especially when used with a variety of applications, such as powertrain-related systems or traction drive systems. Specifically, the present systems and methods are directed to enhancing the accuracy of torque calculations utilized to operate electric motors for a variety of applications.
In one embodiment, a system having an electric motor controller (e.g., traction drive or powertrain-related systems) is disclosed having a field oriented induction motor operating at a detected or inferred stator frequency. The system controller includes an analyzer operable for calculating the torque produced by the motor based on a relationship that is dependent upon the stator frequency. The controlled motor has a first predetermined stator frequency when the system operates at a first predetermined speed and a second predetermined stator frequency when the system operates at a second predetermined speed. The analyzer of the controller calculates the torque using a first algorithm when the controlled motor is at or below the first predetermined stator frequency, a second algorithm when the controlled motor is at or above the second predetermined stator frequency, and a third algorithm when the controlled motor is between the first predetermined stator frequency and the second predetermined stator frequency.
In another embodiment, a method is provided for calculating and supplying the current necessary to provide a specified torque of a field oriented induction motor operating at a given, or measured, stator frequency. The method includes receiving the stator frequency state of the motor (e.g., receiving the stator frequency via inference from a measured current, or a measured speed of a rotor of the motor, or a mechanical load driven by the rotor of the motor) and calculating the current necessary to provide the specified torque by using a first algorithm when the motor is at or below a first predetermined stator frequency. A second, algorithm is utilized to calculate the current necessary to provide the specified torque when the motor is at or above a second predetermined stator frequency, and a third algorithm is utilized to calculate the current necessary to provide the specified torque when the motor is between the first predetermined stator frequency and the second predetermined stator frequency.
In one or more various embodiments, related systems include but are not limited to circuitry and/or programming for effecting the foregoing-referenced method embodiments. The circuitry and/or programming can be virtually any combination of hardware, software, and/or firmware configured to effect the foregoing-referenced method embodiments, depending upon the design choices of the system designer.
In another embodiment, a system for use with an electric powertrain between a field oriented induction motor and a mechanical load is characterized by a torque-control circuit coupleable to respond to a desired-torque input, the torque-control circuit coupleable to infer a stator frequency of the field oriented induction control motor and the torque-control circuit further coupleable to supply a current to the field oriented induction motor, the torque-control circuit configurable to supply the current dependent upon the desired-torque input, the stator frequency, and a combination of an upper-range stator frequency torque equation and a lower-range stator frequency torque equation.
In another embodiment, a motorized vehicle is characterized by a powertrain having an input mechanically coupled to a field oriented induction motor and an output mechanically coupled to a load, the powertrain having a torque-control circuit responsive to a desired-torque input, the torque-control circuit coupled to infer a stator frequency of the field oriented induction control motor and the torque-control circuit further coupled to supply a current to the field oriented induction motor, the torque-control circuit configured to supply the current on the basis of a relationship keyed to at least two predetermined stator frequencies.
The foregoing is a summary and thus contains, by necessity, simplifications, generalizations and omissions of detail; consequently, those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting. Other aspects, inventive features, and advantages of the devices and/or processes described herein, as defined solely by the claims, will become apparent in the non-limiting detailed description set forth herein.